Rice-rapeseed relay cropping is an effective way to use winter fallow fields and increaseland use efficiency. However, the overlapping period of 10–15 days for rice-rapeseedcultivation results in reduced winter survival and less yields. Therefore, in this study, weinvestigated if the treatment of oil rape seeds with paclobutrazol (PAC) improves its winterhardiness and yields by altering its crop morphology. First, a pot experiment was conducted todetermine the appropriate PAC concentration to soak seeds upon seedling growth and thegermination rate. Another pot trial was performed to check the responses of different rapeseedcultivars to the proposed treatment. Rapeseed was cultivated in no-tillage rice fields at anexperimental site in Wuhan from 2009 to 2011. In the absence of PAC treatment, rapeseed sownin pots and rice fields showed excessive elongation of the crown, which resulted in low yieldsand yield-related traits at maturity. Soaking seeds in PAC improved seedling growth, seedlingsurvival and crown diameter, but decreased the crown length during winter. The most effectiveconcentration of PAC was 4 mg/L and higher concentrations significantly reduced seedgermination rates. Our results demonstrated that rapeseed sown in rice fields after the seeds hadbeen soaked with PAC improved seedling quality at the wintering stage and yield at maturity.